In a conventional mobile communication system, Mobile IPv4 (MIPv4) and Mobile IPv6 (MIPv6) are available as mobility management protocols for mobile nodes performing Internet protocol communication (IP communication). These techniques are disclosed in detail in the following Non-Patent Document 1 and Non-Patent Document 2. In order to make MIPv6, which originally operates only in an access network supporting IPv6, operable in an access network supporting IPv4 only as well, Dual Stack Mobile IP (DSMIP) is available, the detailed technique of which is disclosed in Non-Patent Document 3.
Using the MIPv6 protocol based on Non-Patent Document 2, a mobile node registers an IPv6 home address (HoAv6) and an IPv6 care-of address (CoAv6) with a home agent (location management server) and the home agent manages a relationship (binding) between these addresses. Herein, all messages are based on the IPv6 protocol and can be used only from an access network supporting IPv6. The DSMIP is obtained by extending MIPv6, and when a mobile node connects with an access network supporting IPv4 only, an IPv4 care-of address (CoAv4) acquired from the access network is bound with HoAv6, thus enabling communication using HoAv6 from the access network supporting IPv4 only as well.
Provided that the home agent has an IPv4 address, the DSMIP further enables the exchange of a binding control message (Binding Update (BU) or Binding Acknowledge (BA)) based on MIPv6 by encapsulation with an IPv4 header including an address field with CoAv4 and an IPv4 address of the home agent described therein or enables the communication with a correspondent node (CN) having an IPv4 address only by allocating the IPv4 home address (HoAv4) to a mobile node.
The following Patent Document 1 also discloses another method enabling binding management based on MIPv6 for a mobile node connecting with an access network supporting IPv4 only. A handover method using a similar technique is under review in a mobile communication system using mobile phones as well. In the following Non-Patent Document 4, a handover method is disclosed using DSMIP from a 3GPP access network (e.g., LTE) to a non-3GPP access network (e.g., wireless LAN network system, WiMAX network system or a 3GPP2 network system).